Color Blindness: Understanding Red-Green Defects and How They're Inherited

Most people think color blindness means seeing the world in black and white. That’s not true. For the vast majority of people with color vision issues, it’s about red-green color blindness-a condition that doesn’t take away sight, but changes how colors are perceived. It’s not rare. About 8% of men and 0.5% of women worldwide live with it. And it’s not something you develop later in life. You’re born with it. The reason? Your genes.

How Red-Green Color Blindness Works

Your eyes have three types of cone cells that detect color: one for red, one for green, and one for blue. Red-green color blindness happens when the red or green cone cells don’t work right. This isn’t about damaged eyes or poor vision-it’s about faulty pigments inside those cells. These pigments are made by proteins called opsins, coded by two genes: OPN1LW for red and OPN1MW for green. Both sit on the X chromosome, right next to each other.

Here’s the catch: the red gene is usually alone, but there are often multiple green genes lined up after it. During sperm and egg formation, these genes can accidentally swap pieces. If a green gene gets mixed with part of a red gene, it becomes a hybrid that doesn’t respond properly to green light. That’s how most cases of deuteranomaly (the most common form) happen. In rarer cases, one of these genes is just missing entirely, leading to protanopia or deuteranopia-where one color is completely invisible.

People with protanopia can’t see red at all. Reds look dark, almost black. Greens and yellows blend together. Deuteranopes see green as muddy or brownish. Deuteranomaly, the mildest and most common form, means green looks a little off-like it’s washed out. Most people don’t even realize they have it until they’re tested.

Why Men Are Affected More Than Women

Men make up nearly all cases of red-green color blindness. Why? Because of how sex chromosomes work. Men have one X and one Y chromosome. Women have two X chromosomes. The genes for red and green vision are on the X chromosome. So if a man inherits one X with a faulty color gene, he has no backup. He’s affected.

Women need two faulty copies-one on each X chromosome-to have the condition. That’s rare. Even if a woman carries one bad copy, her other X chromosome often compensates. That’s why only about 0.5% of women are affected, compared to 8% of men. It’s not just a coincidence. It’s math: 8% of men being affected means roughly 8% of women carry the gene. But for a woman to be color blind, she needs to inherit the gene from both parents. That happens about once in every 200 women.

This is why you’ll often see color blindness passed from a grandfather to his grandson through his daughter. The daughter doesn’t see it, but she carries it. Her son has a 50% chance of getting the faulty X and being affected.

What Colors Are Hard to Tell Apart?

It’s not just red and green. The real issue is shades that rely on those two colors. Think:

• Red traffic lights vs. green traffic lights-especially in fog or glare
• Green grass vs. red berries
• Brown and orange
• Purple and gray
• Blue and purple

People with red-green color blindness often see these as similar tones. They don’t see them as “wrong”-they just don’t notice the difference. That’s why many go undiagnosed until school, when color-coded lessons trip them up. One study found 78% of adults with the condition struggled with color-coded charts and graphs in class.

Some people adapt brilliantly. A graphic designer in Wellington told me she uses brightness and pattern instead of color to differentiate elements in her designs. “I don’t need to see red and green differently,” she said. “I just need to make sure they’re not the only thing telling the story.”

How It’s Diagnosed

The most common test is the Ishihara test-those plates with colored dots forming numbers. If you can’t see the number, you might have a deficiency. But it’s not perfect. Some people guess correctly by spotting brightness differences. Others pass the test but still struggle in real life.

More accurate tests include the Farnsworth-Munsell 100 Hue Test, which asks you to arrange colored caps in order. Or the anomaloscope, where you mix red and green light to match a yellow. These are used in clinical settings, especially for jobs where color matters: pilots, electricians, train operators.

Many people don’t get tested until they’re applying for a job. One Reddit user, a commercial pilot applicant, wrote: “I had 20/20 vision. I passed every test. But when they showed me the Ishihara plates, I failed. I was disqualified. I didn’t even know I was color blind until then.”

Tools and Adaptations That Help

There’s no cure. But there are tools that make life easier.

EnChroma glasses are the most well-known. They cost between $330 and $500 and filter out overlapping wavelengths of light. For about 80% of people with deuteranomaly or protanomaly, they make colors pop-especially reds and greens. They don’t fix the gene. But they help you see the difference. One user said, “I saw my daughter’s red sweater for the first time and cried.”

Digital tools are just as important. Apple and Windows both have built-in color filters that shift hues to make reds and greens more distinct. The free app Color Oracle lets designers simulate how their work looks to someone with color blindness. The Colorblindifier plugin for Photoshop has been downloaded over 45,000 times.

There’s also ColorADD, a universal symbol system used in 17 countries. It adds simple shapes to colors: a triangle for red, a square for green, a circle for blue. It’s on public transport signs, school materials, and even in pharmacies.

What It Means in Daily Life

Most people with red-green color blindness don’t consider it a disability. In a survey of 850 people, 92% called it a “minor inconvenience.” But the small things add up.

• Choosing clothes that match (37% reported embarrassment over clashing colors)
• Reading color-coded maps or charts
• Identifying ripe fruit or spoiled meat
• Telling if a wire is live (red vs. green in electrical work)

Some careers are harder. Pilots, electricians, firefighters, and graphic designers often face barriers. But laws are changing. The UK’s Equality Act 2010 recognizes color blindness as a disability. Employers must make reasonable adjustments-like labeling wires, using patterns instead of colors, or allowing color filters on screens.

What’s Next? Science and Hope

Research is moving fast. In 2022, scientists at the University of Washington gave gene therapy to adult squirrel monkeys with red-green color blindness. Within weeks, they could see red and green like normal monkeys. The effect lasted over two years.

The National Eye Institute is now funding work to see if the same could work in humans. It’s not about curing it overnight. It’s about giving people back the ability to see the world as most others do.

For now, the best tools are awareness and adaptation. Schools are starting to use patterns in graphs. Websites follow WCAG 2.1 guidelines to ensure color isn’t the only way to convey information. Even Apple and Microsoft now offer color filters built into their operating systems.

Red-green color blindness isn’t a flaw. It’s a variation. And like any variation, it’s best met with understanding-not pity, not correction, but accommodation.